Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B17/00—Surgical instruments, devices or methods, e.g. tourniquets
  • A61B17/56—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor
  • A61B17/58—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor for osteosynthesis, e.g. bone plates, screws, setting implements or the like
  • A61B17/68—Internal fixation devices, including fasteners and spinal fixators, even if a part thereof projects from the skin
  • A61B17/70—Spinal positioners or stabilisers ; Bone stabilisers comprising fluid filler in an implant
  • A61B17/7001—Screws or hooks combined with longitudinal elements which do not contact vertebrae
  • A61B17/7041—Screws or hooks combined with longitudinal elements which do not contact vertebrae with single longitudinal rod offset laterally from single row of screws or hooks
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B17/00—Surgical instruments, devices or methods, e.g. tourniquets
  • A61B17/56—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor
  • A61B17/58—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor for osteosynthesis, e.g. bone plates, screws, setting implements or the like
  • A61B17/68—Internal fixation devices, including fasteners and spinal fixators, even if a part thereof projects from the skin
  • A61B17/70—Spinal positioners or stabilisers ; Bone stabilisers comprising fluid filler in an implant
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B17/00—Surgical instruments, devices or methods, e.g. tourniquets
  • A61B17/56—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor
  • A61B17/58—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor for osteosynthesis, e.g. bone plates, screws, setting implements or the like
  • A61B17/68—Internal fixation devices, including fasteners and spinal fixators, even if a part thereof projects from the skin
  • A61B17/70—Spinal positioners or stabilisers ; Bone stabilisers comprising fluid filler in an implant
  • A61B17/7001—Screws or hooks combined with longitudinal elements which do not contact vertebrae
  • A61B17/7035—Screws or hooks, wherein a rod-clamping part and a bone-anchoring part can pivot relative to each other

Definitions

• This invention relates generally to a polyaxial pedicle screw for use with orthopedic fixation systems having modular components More particularly, the present invention relates to a screw for insertion into the vertebral bone having a shaft and a set of modular coupling elements which are polyaxially mounted thereto, via a stem member which is flexibly connected to the top portion of the shaft portion, therein enhancing the efficacy of the implant assembly by providing freedom of angulation among the rod, shaft and modular elements
• the bones and connective tissue of an adult human spinal column consists of more than 20 discrete bones coupled sequentially to one another by a tri-joint complex which consist of an anterior disc and the two posterior facet joints, the anterior discs of adjacent bones being cushioned by cartilage spacers referred to as intervertebral discs
• intervertebral discs Referring now to Figures 1, 2, and 3, top, side, and posterior views of a vertebral body, a pair of adjacent vertebral bodies, and a sequence of vertebral bodies are shown, respectively
• the spinal cord is housed in the central canal 10, protected from the posterior side by a shell of bone called the lamina 12
• the lamina 12 includes a rearwardly and downwardly extending portion called the spinous process 16, and laterally extending structures which are referred to as the transverse processes 14
• the anterior portion of the spine comprises a set of generally cylindrically shaped bones which are stacked one on top of the other These portions of the vertebrae are referred to as the vertebral bodies 20,
• Rod assemblies generally comprise a plurality of such screws which are implanted through the posterior lateral surfaces of the laminae, through the pedicles, and into their respective vertebral bodies These screws are typically provided with upper portions which comprise coupling means, for receiving and securing an elongate rod therethrough
• the rod extends along the axis of the spine, coupling to the plurality of screws via their coupling means
• the rigidity of the rod may be utilized to align the spine in conformance with a more healthful shape
• the Isola(TM) system which is produced by Acromed, suffers from many of these failures in as much as it does not provide the surgeon to freely angulate the rod coupling means of the screw to meet the rod
• the Isola system consists of a shaft portion which is to be inserted into the patient's pedicle, the shaft having a threaded stem portion rigidly extending upwardly from the top of the shaft portion (The interface of the shaft portion and the stem portion includes a hexagonally shaped annulus for engagement with a torque wrench to permit insertion )
• the principal object of the present invention to provide a pedicle screw and coupling element assembly which provides a polyaxial freedom of implantation angulation with respect to rod reception.
• the polyaxial screw assembly of the present invention comprises two alternative embodiments.
• the first embodiment includes a threaded shaft portion for insertion into the pedicle, the top of shaft portion including a bowl- shaped socket and a second threading; a stem portion having a threading, corresponding to the second threading, for receiving spacer elements and/or a rod coupling element thereon, the bottom of said stem portion including a ball (semi-spherical section), and a cylindrical locking cuff which is mounted about the top of the shaft and the bottom of the stem to secure the ball of the stem in the bowl-shaped socket of the shaft
• the second embodiment includes a threaded shaft portion for insertion into the pedicle, the top of shaft portion including a convex top and a second threading, a stem portion having a threading, corresponding to the second threading, for receiving space
• the shaft portion includes an elongate shank portion having the threading of a bone screw (standard or otherwise, but suited for proper purchase of the bone)
• the uppermost portion of the shaft comprises a bowl-shaped recess which forms a socket
• This socket portion may be greater or less than a fully hemispherical recess
• axial slots need to be provided so that the ball may be slipped into the socket
• a small hexagonal bore may be disposed in the based of the bowl-shaped socket, coaxial with the shaft, so that a screw driving device (alien wrench, etc ) may be utilized to insert the shaft into the bone
• a widened annular portion of the shaft, disposed between the two threadings may be hexagonal so as to permit the use of a torque wrench or other surgical tool
• the axial surface of the shaft at the top (socket) end includes the second threading, for receiving and locking the cuff element thereto
• the stem comprises an elongate post portion having an enlarged ball (having a larger diameter than the post portion) formed at the bottom thereof, the enlarged ball having substantially the same radius of curvature as the bowl- shaped socket portion of the shaft Therefore, when the ball is initially placed in the bowl-shaped socket, the stem may be positioned in a variety of different angulations relative to the axis of the shaft portion (through a polyaxial range of configurations from coaxial to substantially non-coaxial)
• the securing cuff comprises a hollow cylindrical body, having a threading on the bottom half (halves being defined relative to the through axis) of the interior surface thereof This threading is designed to mate with the threading on the uppermost portion of the shaft element
• the upper half of the interior surface of the cuff may comprise a semi-spherical taper when used in conjunction with a shaft which has a socket which is less than hemispherical
• the top end of the cuff need not be tapered on the inside
• the inner diameter of the open end of the top of the cuff is larger than the diameter of the post portion of the stem, but more narrow than the diameter of the ball formed at the bottom end of the stem
• a portion of the exterior of the cuff comprises a hexagonally angled surface contour, such that the cuff may be easily engaged by a torque wrench (It shall be understood that any one of a variety of such surface contours or other means may be employed equivalently )
• the upper exterior of the cuff is rounded (with a constant radius of curvature) so that it provides a curvate profile This permits the secure engagement of similarly rounded spacer elements relative to the top of the cuff element independent of the angular orientation of the post portion of the stem relative to the cuff and shaft
• spacer elements may also be utilized
• the spacers are annular elements having a diameter which is equivalent to that of the post portion (and are preferrably threaded)
• the bottom surfaces of the spacer elements are concave, having a radius of curvature equal to that of the upper surface of the cuff As stated above, this mutual contour permits the spacer to seat securely against the cuff independent of the angulation of the stem
• the upper surface of the spacer element is convex, having an equivalent radius of curvature, such that multiple spacers may be nested
• the advancing the spacer elements downwardly on the stem, and into contact with the cuff, and subsequent tightening causes an increase in the total locking force applied to the ball in the socket (the ball is pulled into tighter contact with the socket-shaped interior of the cuff)
• the outer lateral surface of the elements are contoured so as to be engageable by a torque wrench, e g , having a hexagonal shape
• the rod coupling element of this assembly comprises a flat portion having an elongate hole therethrough for coupling to the stem, and a tubular portion which may be slideably advanced along the rod into the proper position Once in the proper position, the rod coupling means is locked to the rod by a set screw in order to prevent further movement relative to the rod
• the elongate hole in the flat portion is elongate in nature so that distance from the rod to the stem may be varied
• This element further includes the concave conformation on the underside thereof so that it may nest securely on the upper surface of either a spacer or directly on the cuff (in the case wherein no spacer
• the shaft portion includes an elongate shank portion which is similar to that of the first embodiment insofar as it has the threading of a bone screw (standard or otherwise, but suited for proper purchase of the bone)
• the uppermost portion of this shaft comprises a hemisphe ⁇ cally curved convex bubble This portion may be less than a full hemisphere, but a full hemisphere is preferred
• a small hexagonal bore may be disposed in the axial center of the hemisphere, coaxial with the shaft, so that a screw driving device (alien wrench, etc ) may be utilized to insert the shaft into the bone
• a widened annular portion of the shaft, disposed between the two threadings may be hexagonal so as to permit the use of a torque wrench or other surgical tool
• the lateral (circumferential) surface of the shaft at the top end includes the second threading, for receiving and locking the cuff element thereto
• the stem of the second embodiment comprises an elongate post portion having an enlarged lower portion which includes a spherically concave recess formed in the bottom thereof
• the recess has substantially the same radius of curvature as the hemispherical upper portion of the shaft Therefore, when the recess is initially permitted to nest on the hemisphere, the stem may be positioned in a variety of different angulations relative to the axis of the shaft portion (through a polyaxial range of configurations from coaxial to substantially non-coaxial)
• the securing cuff comprises a hollow cylindrical body, having a threading on the bottom half (halves being defined relative to the through axis) of the interior surface thereof This threading is designed to mate with the threading on the uppermost circumferential portion of the shaft element
• the upper half of the interior surface of the cuff comprises a contour, preferably a semi-spherical taper which forms an open ended socket.
• the inner diameter of the open end of the top of the cuff is larger than the diameter of the post portion of the stem, but more narrow than the diameter of the lower socket portion formed at the bottom end of the stem.
• a portion of the exterior of the cuff comprises a hexagonally angled surface contour, such that the cuff may be easily engaged by a torque wrench (It shall be understood that any one of a variety of such surface contours or other means may be employed equivalently )
• the upper exterior of the cuff is rounded (with a constant radius of curvature) so that it provides a curvate profile This permits the secure engagement of similarly rounded spacer elements relative to the top of the cuff element independent of the angular orientation of the post portion of the stem relative to the cuff and shaft (the cuff and shaft remain coaxial) More particularly, inasmuch as it is still desirable to permit variable positioning of the rod coupling means along the axis of the stem, in addition to the angular variability provided by the polyaxial shaft-stem-cuff assembly, spacer elements may also be utilized
• the spacers are annular elements having a diameter which is equivalent to that of the post portion (and are preferrably threaded)
• the advancing the spacer elements downwardly on the stem, and into contact with the cuff, and subsequent tightening causes an increase in the total locking force applied to the socket on the hemisphere (the external surface of the lower socket portion of the stem is pulled more tightly into contact with the socket formed by the interior of the cuff)
• the outer lateral surface of the elements are contoured so as to be engageable by a torque wrench, e g , having a hexagonal shape
• the rod coupling element of this assembly comprises a flat portion having an elongate hole therethrough for coupling to the stem, and a tubular portion which may be s deably advanced along the rod into the proper position Once in the proper position, the rod coupling means is locked to the rod by a set screw in order to prevent further movement relative to the rod
• the elongate hole in the flat portion is elongate in nature so that distance from the rod to the stem may be varied
• This element further includes the concave conformation on the underside thereof so that it may nest securely on the upper surface of either a spacer or directly on the cuff (in the case wherein no spacer is used)
• the first step in the process of implanting this invention in either embodiment is to pre-drill the appropriate site in the pedicle to receive the shaft The shaft is then driven into the vertebral body The cuff is then advanced down the stem portion until it reaches the ball or socket portion The ball and socket portions are then placed together such that they may rotate relative to one another, and the threadings
• the stem is then angulated into the appropriate position, and the cuff is locked down, thereby securing the stem relative to the shaft
• the rod coupling element is then slideably advanced along the rod into the appropriate position, and the stem placed in the elongate hole thereof
• the set screw of the rod coupling element is engaged to lock thereto. (Spacers are threadably advanced onto the stem prior to the insertion of the stem through the elongate hole, if it is determined that they are necessary )
• the top locking nut is advanced downwardly along the stem and into position against the top of the rod coupling element, thereby preventing any lateral or axial movement of the stem within the elongate hole
• screw and coupling element assembly of the present invention is designed to be compatible with alternative rod systems so that, where necessary, the present invention may be employed to rectify the failures of other systems the implantation of which may have already begun
• Figure 1 is a top view of a human vertebra, which is representative of the type for which the present invention is useful for coupling thereto a rod apparatus
• Figure 2 is a side view of a pair of adjacent vertebrae of the type shown in Figure 1 ,
• Figure 3 is a posterior view of a sequence of vertebrae of the type shown in Figures 1 and 2,
• FIGS 4a and 4b are side cross section views of alternative threaded shafts which are aspects of the present invention.
• Figure 5 is a side view of a stem portion, having a ball formed at the bottom thereof, which is an aspect of the present invention
• Figures 6a and 6b are side cross section views of alternative cuffs of the present invention.
• Figure 7 is a side cross section view of a spacer element which is an aspect of the present invention.
• Figure 8 is a perspective view of a rod coupling element which is an aspect of the present invention.
• Figure 9 is a side cross-sectional view of the top locking nut of the present invention.
• Figures 10a and 10b are side views of two fully assembled modular polyaxial pedicle screws of the present invention.
• Figure 11 is a side cross section view of a threaded shaft which is another aspect of the present invention.
• Figure 12 is a side view of a stem portion, having a socket formed at the bottom thereof, which is an aspect of the present invention
• Figure 13 is a side cross section views of a cuff element of the present invention
• Figure 14 is a side cross section view of a spacer element which is an aspect of the present invention
• Figure 15 is a perspective view of a rod coupling element which is an aspect of the present invention.
• Figure 16 is a side cross-sectional view of the top locking nut of the present invention.
• Figure 17 is a side view of a fully assembled modular polyaxial pedicle screw of the present invention
• the alternative modular polyaxial pedicle screws of the present invention first comprises a threaded shaft portion 100a, 100b which is inserted into the pedicle
• Both shafts 100a, 100b include a lower shank portion 102 which include a bone screw threading 104 (This threading 104 may be standard or otherwise, but is in any case suited for necessary purchase of bone )
• the top 106a of the shaft 100a comprises a bowl-shaped recess 108a which forms a socket
• This socket 108a comprises less than a hemispherical section
• the top 106b of the shaft 100b may comprise a socket 108b which is greater than a hemispherical section.
• the upper lip 109 thereof should include at least one axial slot 1 1 1 which extends below the maximum diameter A-A, and which may expand and contract in accordance with the application of a radial
• the axial surfaces of the upper ends 1 10a, 1 10b of the shafts 100a, 100b include a second threading 1 12 A widened hexagonal annulus 1 14, which is integrally formed with the shaft 100a, 100b, and is disposed between the threaded shank 102 and upper portions 1 10a, 1 10b, is provided so that a suitable torque wrench may be employed to drive the shaft 100a, 100b into the vertebral body through the pedicle.
• a stem portion 120 is shown in a side view More specifically, the stem 120 comprises an elongate threaded post portion
• the ball 124 has a larger diameter than the post 122.
• the ball 124 has substantially the same radius of curvature as the bowl- shaped socket 108 portion of the shaft 100 This mutual dimension permits the ball 124 to rotate freely in the socket 108 once the ball 124 is placed therein, thus permitting the stem 120 to be angulated relative to the shaft 100 (through a polyaxial range from coaxial to substantially non-coaxial)
• the mutual engagement of the shafts 100a, 100b with the stem 120 is provided by corresponding cuffs 130a, 130b, shown in side cross section views
• the cuffs 130a, 130b are each hollow cylinders and have a threading 132 on the bottom half of the interior surface
• the upper half of the interior surface 136 of the cuff 130a comprises a semi-spherical taper, which forms an open ended socket
• the embodiment which is to be utilized with the shaft 100b having a socket 108b which defines greater than a hemisphere has no internal taper at the upper end, however, the lower threaded portion may include a reverse taper, i e narrower at the top, in order to provide an inwardly directed radial force onto the upper lip 109
• the inner diameter B-B of the open end 138 of the top of the cuff 130a, 130b is larger than the diameter of the threaded post portion 122 of the stem 120
• the stem 120 and shaft 100a, 100b portions are initially held coaxial, with the ball 124 of the stem 120 in the socket 108a, 108b of the shaft 100a, 100b (the ball 124 being snapped into the socket 108b by applying a downward force whereby the at least one slot 11 1 expands), while the securing cuff 130a, 103b is advanced down along the post portion of the stem until the threadings 132,112 of the cuff 130a, 130b and the uppermost exterior surface 1 10a, 110b of the shaft, respectively, engage
• the stem 120 and shaft 100a, 100b are thereby loosely held together by the cuff 130a, 130b, respectively, but each may be angulated relative to the other by virtue of the ball 124 and socket 108a, 108b interface
• the total range of angulation is established by the relative diameters of the ball 124, the post 122, (the upper lip 109 of the socket 108b), and the opening 138 at the top of
• a portion of the exterior 140 of the cuff 130a, 130b comprises a hexagonally angled surface contour, such that the cuff 130a, 130b may be easily engaged by a torque wrench
• the upper exterior 142 of the cuff 130a, 130b is rounded (with a constant radius of curvature) so that it provides a curvate profile This permits the secure engagement of similarly rounded spacer elements (see Figure 7, and related description hereinbelow) relative to the top of the cuff 130a, 13 Ob independent of the angular orientation of the post 122 of the stem 120 relative to the cuff 130a, 13 Ob and shaft
• spacer elements 150 are provided The spacers 150 are annular elements having an inner diameter C-C which is equivalent to that of the post 122
• the inner surface 152 includes a threading 154 which is engageable with the threading of the post 122 (It is not necessary for the spacers 150 to be threaded, however, such a threading may provide additional downward force on the cuff 130a, 130b to further secure the locking of the stem 120 and the shaft 100a, 100b )
• the bottom surface of the spacer 150 is concave, having a radius of curvature equal to that of the tapered upper portion 142 of the cuff 130a, 130b This mutual contour permits the spacer 150 to seat securely against the cuff 130a, 130b independent of the angulation of the stem 120
• the upper surface 142 of the spacer 150 is conve
• the rod coupling element 160 of this assembly comprises a flat portion 162 having an elongate hole 164 therethrough for coupling to the stem 120
• the elongate hole 164 has a width equal to that of the post 122, but is elongated to permit variable lateral placement of the post 122 relative to the rod 200
• the edge (not seen in this illustration) of the elongated hole 164, on the underside of the flat portion, is concavely tapered so as to ideally receive the curvate upper portion of the spacer 150 or the cuff 130a, 130b
• the rod coupling element 160 further includes a tubular portion 166, the axis of the tube is substantially perpendicular to the elongated axis of the hole 164
• the rod coupling element 160 is positioned on the rod 200 by slideably advancing it therealong Once in the proper position, the rod coupling element 160 is locked to the rod 200 by a set screw 168 in order to prevent further movement relative to the rod
• this element 160 further includes a concave underside conformation 170 such that it may nest securely on the upper surface of either a spacer 150 or directly on the cuff 130a, 130b (in the case wherein no spacer 150 is used)
• a top locking nut 170 is utilized to lock the rod coupling element 160 onto the post 122 More particularly, the top locking nut 170 has a bottom surface 172 which is ideally suited to engage and hold the post 122 and the rod coupling element 160 from axial or lateral movement Specifically, the top locking nut 170 is designed to apply a downward pressure which is sufficient to lock the cuff 130a, 130b into the tapered curvate edge of the elongate hole 164 such that the friction locking force of the spacer 150 or cuff 130a, 130b thereagainst is sufficient to hold the rod coupling element 160 from lateral, or axial, movement
• a hole is pre-drilled in the appropriate site in the pedicle in order to receive the shaft 100a, 100b
• the shaft 100a, 100b is then driven into the vertebral body
• the cuff 130a, 130b is then advanced down the stem 120 until it reaches the ball 124
• the ball 124 is then placed (or snapped) into the socket 108a, 108b, and the threadings 1 12, 132 on the upper portion 1 10a, 1 10b of the shaft 100a, 100b and on the interior of the cuff 130a, 130b, respectively, are engaged
• the post 122 is then angulated into the appropriate position, and the cuff 130a, 13 Ob is locked down, thereby securing the stem 120 relative to the shaft 130a, 13 Ob (The ball 124 is crush locked between the cuff 130a and the socket 108a Alternatively, the ball 124 is crushed into the socket 108b by virtue of the socket itself being collapsed onto the ball 124
• a complete posterior rod implant system includes at least two, and generally four or more, screw assemblies
• this assembly as set forth above, may also be used in conjunction with other screw assemblies in the art wherein there is an immediate need for the beneficial properties of this assembly to correct deficiencies in the other assemblies Therefore, it is anticipated that this modular polyaxial pedicle screw may be used individually, or in conjunction with others
• the modular polyaxial pedicle screw of the present invention first comprises a threaded shaft portion 300 which is inserted into the pedicle
• the shaft 300 includes a lower shank portion 302 which include a bone screw threading 304 (This threading 304 may be standard or otherwise, but is in any case suited for necessary purchase of bone )
• the top 306 of the shaft 300 comprises a hemispherical protuberance 308 which forms an upper rounded surface
• the circumferentail surfaces of the upper end 310 of the shaft 300 (around the hemisphere 308) includes a second threading 312 A widened hexagonal annulus 314, which is integrally formed with the shaft 300, and is disposed between the threaded shank 302 and upper portion 310, is provided so that a suitable torque wrench may be employed to drive the shaft 300 into the vertebral body through the pedicle
• the stem 320 comprises an elongate threaded post portion 322 and an enlarged lower socket portion 323
• the lower portion 323 has a larger diameter than the post 322 and includes a spherical recess 324 formed in the bottom thereof
• the recess 324 has substantially the same radius of curvature as the hemispherical upper portion 308 of the shaft 300 This mutual dimension permits the recess 324 to rotate freely over the hemispherical upper portion 308 once the socket 324 is nested thereon, thus permitting the stem 320 to be angulated relative to the shaft 300 (through a polyaxial range from coaxial to substantially non-coaxial)
• the cuff 330 is a hollow cylinder and has a threading 332 on the bottom half of the interior surface 334 thereof This threading 332 is designed to mate with the threading 312 on the uppermost portion 310 of the shaft element 300
• the upper half of the interior surface 336 of the cuff 330 comprises a curvate taper, which is preferably semi-spherical and forms an open ended socket
• the inner diameter of the open end 338 of the top of the cuff 330 is larger than the diameter of the threaded post portion 322 of the stem 320, but more narrow than the diameter of the lower socker portion 323
• the stem 320 and shaft 300 portions are initially held coaxial, with the recess 324 of the stem 320 on the hemispherical upper portion 308 of the shaft3100, while the securing cuff 330 is advanced down along the post portion of the stem until the threadings 332,312 of the cuff 330 and the uppermost exterior surface 310 of the shaft engage
• the stem 320 and shaft 300 are thereby loosely held together by the cuff 330, but each may be angulated relative to the other by virtue of the geometry of the recess 324 and hemispherical upper portion 308 interfacing
• the total range of angulation is established by the relative diameters of the hemispherical upper portion 308, the lower socker portion of the stem, the post 322, and the opening 338 at the top of the cuff
• Complete tightening of the cuff 330 causes the recess 324 to be crushed onto the hemispherical upper portion 308, thereby preventing any further
• a portion of the exterior 340 of the cuff 330 comprises a hexagonally angled surface contour, such that the cuff 330 may be easily engaged by a torque wrench
• the upper exterior 342 of the cuff 330 is rounded (with a constant radius of curvature) so that it provides a curvate profile This permits the secure engagement of similarly rounded spacer elements (see Figure 14, and related description hereinbelow) relative to the top of the cuff 330 independent of the angular orientation of the post 322 of the stem 320 relative to the cuff 330 and shaft 300
• spacer elements 350 are provided The spacers 350 are annular elements having an inner diameter D-D which is equivalent to that of the post 322
• the inner surface 352 includes a threading 354 which is engageable with the threading of the post 322 (It is not necessary for the spacers 350 to be threaded, however, such a threading may provide additional downward force on the cuff 330 to further secure the locking of the stem 320 and the shaft 300 )
• the bottom surface of the spacer 350 is concave, having a radius of curvature equal to that of the tapered upper portion 342 of the cuff 330 This mutual contour permits the spacer 350 to seat securely against the cuff 330 independent of the angulation of the stem 320.
• the upper surface 342 of the spacer 350 is convex, having an equivalent radius of curvature, such that multiple spacers 350 may be nested.
• the outer lateral surface 356 is contoured so as to be engageable by a torque wrench; e.g., having a hexagonal shape.
• the rod coupling element 360 of this assembly comprises a flat portion 362 having an elongate hole 364 therethrough for coupling to the stem 320.
• the elongate hole 364 has a width equal to that of the post 322, but is elongated to permit variable lateral placement of the post 322 relative to the rod 200.
• the edge (not seen in this illustration) of the elongated hole 364, on the underside of the flat portion, is concavely tapered so as to ideally receive the curvate upper portion of the spacer 350 or the cuff 330.
• the rod coupling element 360 further includes a tubular portion 366, the axis of the tube is substantially perpendicular to the elongated axis of the hole 364.
• the rod coupling element 360 is positioned on the rod 200 by slideably advancing it therealong. Once in the proper position, the rod coupling element 360 is locked to the rod 200 by a set screw 368 in order to prevent further movement relative to the rod.
• this element 360 further includes a concave underside conformation 370 such that it may nest securely on the upper surface of either a spacer 350 or directly on the cuff 330 (in the case wherein no spacer 350 is used).
• a top locking nut 370 is utilized to lock the rod coupling element 360 onto the post 322. More particularly, the top locking nut 370 has a bottom surface 372 which is ideally suited to engage and hold the post 322 and the rod coupling element 360 from axial or lateral movement Specifically, the top locking nut 370 is designed to apply a downward pressure which is sufficient to lock the cuff 330 into the tapered curvate edge of the elongate hole 364 such that the friction locking force of the spacer 350 or cuff 330 thereagainst is sufficient to hold the rod coupling element 360 from lateral, or axial, movement
• a complete posterior rod implant system includes at least two, and generally four or more, screw assemblies
• this assembly as set forth above, may also be used in conjunction with other screw assemblies in the art wherein there is an immediate need for the beneficial properties of this assembly to correct deficiencies in the other assemblies Therefore, it is anticipated that this modular polyaxial pedicle screw may be used individually, or in conjunction with others.

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• Health & Medical Sciences (AREA)
• Orthopedic Medicine & Surgery (AREA)
• Life Sciences & Earth Sciences (AREA)
• Neurology (AREA)
• Surgery (AREA)
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• General Health & Medical Sciences (AREA)
• Biomedical Technology (AREA)
• Heart & Thoracic Surgery (AREA)
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• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Animal Behavior & Ethology (AREA)
• Engineering & Computer Science (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Surgical Instruments (AREA)
• Polyesters Or Polycarbonates (AREA)
• Infusion, Injection, And Reservoir Apparatuses (AREA)
• Earth Drilling (AREA)
• Non-Disconnectible Joints And Screw-Threaded Joints (AREA)
• Thermotherapy And Cooling Therapy Devices (AREA)

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Cited By (41)

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• 1997
  • 1997-10-07 EP EP97945561A patent/EP0949887B1/de not_active Expired - Lifetime
  • 1997-10-07 DE DE69737034T patent/DE69737034T2/de not_active Expired - Lifetime
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  • 1997-10-07 WO PCT/US1997/018155 patent/WO1998015233A1/en active IP Right Grant
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  • 1997-10-07 KR KR10-1999-7003041A patent/KR100531146B1/ko not_active IP Right Cessation
• 2007
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